Long before the term was used to describe talent-free people in the public eye, John Betjeman was a celebrity: Poet Laureate, saviour of ancient buildings and National Treasure. But though his wife Penelope is affectionately portrayed in his letters, and in a biography by their granddaughter Imogen Lycett-Green, for me she always remained an enigma. Until, that is, I was cast to play her in a BBC Radio production and discovered the first of her two books, Two Middle-Aged Ladies in Andalusia (1963).